Application of Vadium Dioxide (VO2) based pixels for electrically modulating light utilizing the phase transition property of VO2 is well known in the art. VO2 exhibits an insulator-to-metal phase transition at a temperature T.sub.c =68.degree. C. which is accompanied by a significant change in electrical and optical properties. Due to this feature, this material has been utilized in various electrical and optical applications. These applications have included: a medium for holographic optical recording, a temperature stabilizer and controller, an electronic switch, material for screening and modulating microwave radiation and electronic and optical memory elements. One of the optical properties which is significantly changed during the phase transition is the index of refraction, which enables VO.sub.2 to modulate light reflectance. The phase transition in VO.sub.2 can be thermally induced by utilizing heater elements disposed under the film of this material. This feature can be utilized in the flat panel displays. An example of such a phase transition flat panel display is described in co-pending patent application Ser. No. 08/791,032 entitled "Phase Transition Flat Panel Display", incorporated herein by reference.
The prior art phase transition flat panel display comprises a plurality of individual VO2 based pixels, arranged in a conventional two dimensional matrix array fabricated on silicon substrates. Each pixel includes an optical resonator comprising a film of VO2 disposed on top of an aluminum mirror element. A film of polysilicon is disposed beneath the mirror element and acts as a heater element to heat the VO2 film to cause the phase transition of the pixel. An air gap is provided between the polysilicon heater film and the silicon substrate layer to minimize heat dissipation through the substrate. Each pixel is interconnected by column and a row line. A diode is coupled to each pixel and implemented as a pn junction fabricated on the silicon substrate. These diodes are utilized to prevent current spread and possible cross talk between the pixel elements.
While the prior art phase transition display has been proposed to provide high speed processing for video frequency operation, high resolution, gray levels, and color display, its manufacturing is rather complex. First, to make the temperature decay time as long as possible and thus minimize the display power consumption, each pixel is fabricated as a membrane disposed over the air gap in the Si substrate. Moreover, to further increase the decay time, the display must operate in a vacuum. Both these factors complicate the device manufacturing and increase production cost. Second, the pixel heaters are planned to be fabricated from poly-silicon. This requires display heating for poly-Si anneal and implantation to temperatures as high as 900.degree. C. and thus makes it incompatible with the driving circuitry, which is designed to be fabricated on the same Si wafer prior to the pixel processing. Accordingly, an improved pixel structure for a phase transition display device which overcomes these problems is greatly desired.